The predominant interior package cushioning material currently used in the packaging of products for shipping and distribution is plastic. Such plastic cushioning materials include a variety of polyethylene foams, moldable polyethylene copolymer foam, expanded polyethylene bead foam, styrene acrylonitrile copolymer foam, polystyrene foams, polyurethane foams, etc. Such plastic materials and plastic foams may be molded in place or molded to specific interior package cushioning structure shapes. The plastic may be formed in pieces to provide loosefill. Sheets of plastic film may be bonded together encapsulating bubbles of air to provide cushioning material. Such plastic interior package cushioning materials are described for example in Brandenburg and Lee, Fundamentals of Packaging Dynamics, MTS Systems, P.O. Box 24012, Minneapolis, Minn. 55424 (1985), Singh, Charnnarong, and Burgess "A Comparison Between Various Package Cushioning Materials", IOPP Technical Journal, (Journal of the Institute of Packaging Professionals) Winter 1992 issue, pages 28-36, and U.S. Pat. Nos. 5,096,650 and 4,792,045.
There are two major disadvantages associated with plastic cushioning materials and plastic interior package cushioning structures. Disposable packaging is a major contributor to the nation's municipal solid waste. It is estimated that packaging constitutes approximately one third by volume of all municipal solid waste and 8% of this amount is made up of the cushioning materials. The plastic cushioning materials are generally neither biodegradable nor compostable and therefore remain a long term component of the solid waste accumulation problem.
Furthermore because of the nature of plastic molecules the plastic interior package cushioning structures are characterized by irreducible spring constant parameters that may be detrimental to product cushioning and to product protection from mechanical shock and vibration during shipping and distribution of packaged products. Plastic foam materials may be inherently limited in the reduction that can be achieved for rebound, coefficient of restitution, and elasticity. As a result, the plastic cushioning materials may be implicated in resonance conditions which increase the shock amplification factor of the package system and link the shock acceleration, change of velocity and displacement with a product contained in the package. With respect to mechanical shock and impact imparted to a package by corner drops, edge drops and face drops, falling onto the floor and horizontal impacts, the plastic interior package cushioning structures of the product/package system may, if such resonance conditions occur, contribute to undesirable shock transmission and shock amplification. The shock amplification factor introduced by plastic cushioning materials may actually increase the shock accelerations, changes in velocities, and displacements experienced by a product.
Similarly with respect to mechanical vibrations imparted by shipping vehicles and other transport modes, the plastic interior package cushioning structures of the package/product system may under resonance conditions contribute to vibration magnification or transmissibility. The vibration magnification factor of plastic cushioning materials may result in a multiples increase in the vibration accelerations, changes in velocity, and displacements experienced by the packaged product. Again, it is the characteristics of plastic cushioning materials that contribute to resonance conditions enhancing the vibration magnification factor and linking the forcing vibrations of the transport mode with a product inside the package.
Another disadvantage of plastic foam interior package cushion structures is that the inherent rebound, coefficient of restitution, modules of elasticity, and spring constant characteristics of the plastic materials are an impediment to achieving critical damping structures for critically damping mechanical shocks and shipping vibrations. The plastic foam filled spaces conventionally used in product packaging may contribute to conditions of overdamping or underdamping with excessive transmissibility of mechanical shock and vibration accelerations, changes in velocity, and displacements to the packaged product.
Molded pulp fiber has previously been used in packaging structures described in U.S. Pat. Nos. 5,096,650; 4,742,916; 4,480,781; 4,394,214; 3,718,274; 3,700,096; 3,286,833; 3,243,096; 2,704,268. For example, Keyes Fiber Company, College Avenue, Waterville, Me. 04901 manufactures molded fiber fluorescent tube trays used in shipping fluorescent tubes stacked in a package. The fluorescent tube trays are formed with recesses complementary with the cylindrical fluorescent tubes. However these prior art fluorescent tube trays function only as dividers for preventing glass to glass contact. To the extent that the fluorescent tube trays can be described as being formed with recesses or ribs, the recesses only perform an indexing function for separating the tubes from one another.
The Keyes Fiber Company fluorescent tube trays do not perform a stacking function in the sense of directing stacking forces around product receiving recesses. Rather the tube trays do not contact each other and the stacking forces bear directly on the fluorescent tubes. Furthermore the fluorescent tube trays do not perform a design cushioning or design protection function. They are not designed to crush and absorb energy at package accelerations caused by mechanical shock and vibration which approach a specified design threshold or limit of mechanical shock and vibration acceleration at which damage or breakage may occur to a sensitive element of the fluorescent tube products shipped in the package. The utility of such fluorescent tube trays is exhausted by the dividing, indexing and separating functions only.
Another common molded pulp fiber package structure is the egg crate. Egg crates are typically formed with egg pockets for containing, indexing and separating the eggs. Resilient pillow pads or buttons may be formed in the bottom of egg pockets to "cradle" eggs in the egg pockets. The egg crate cover rests on "posts" formed at the intersections between egg pockets for bearing stacking forces so that egg crates may be stacked. However, the egg pockets and related structures of a conventional egg crate are not designed to crush and absorb energy for protecting eggs at package design limit or design threshold accelerations. Conventional egg crates do not incorporate crushable structures intended to crush and absorb energy at package accelerations from mechanical shock and vibration which approach a specified design threshold or limit at which damage or breakage may occur to eggs. The primary purpose for egg crates as for molded pulp fiber apple flats and other molded pulp fiber trays for food products is for indexing, dividing, orienting, and separating products from contact with each other. On the other hand, the present invention is directed to molded pulp fiber packaging structures specifically intended, designed, and constructed to meet predictable and reliable design specifications and cushioning requirements for protecting products shipped in a package from specified levels of mechanical shock and vibration accelerations at which damage or breakage may occur to a sensitive element of products shipped in a package.
Packaging structures have also been manufactured by so-called "slush molding" from a Kraft fiber based raw material slurry. Such Kraft fiber slush molded packaging structures are manufactured by Fibercel Inc. of Portville, N.Y. The heavy Kraft fiber structures are vacuum molded by "candle dipping", that is by immersion of the vacuum molding head multiple times in the slurry. A disadvantage of the slush molded package structures is that they are relatively rigid structures that are not predictably crushable. They cannot crush and absorb energy at reliable specified design limits or thresholds of mechanical shock and vibration acceleration. They are primarily intended for blocking and bracing and also are not suitable for nesting because of the mass of the slush molded structures.